The present invention relates generally to golf club heads and, more particularly, to golf club heads having an improved face construction.
Modern golf clubs have typically been classified as woods, irons or putters. Additionally, a newer class of golf clubs termed xe2x80x9cutilityxe2x80x9d clubs or xe2x80x9ciron woodsxe2x80x9d seek to replace low lofted long irons or higher numbered fairway woods. The term xe2x80x9cwoodxe2x80x9d is an historical term that is still commonly used, even for golf clubs that are constructed of steel, titanium, fiberglass and other more exotic materials, to name a few. The woods are now often referred to as xe2x80x9cmetal woods.xe2x80x9d The term xe2x80x9cironxe2x80x9d is also an historical term that is still commonly used, even though those clubs are not typically constructed of iron, but are rather constructed of many of the same materials used to construct xe2x80x9cwoodsxe2x80x9d.
One particular improvement that relates especially to metal woods is the use of lighter and stronger metals, such as titanium. A significant number of the premium metal woods, especially drivers, are now constructed primarily using titanium. The use of titanium and other lightweight, strong metals has made it possible to create metal woods of ever increasing sizes. The size of metal woods, especially drivers, is often referred to in terms of volume. For instance, current drivers may have a volume of 300 cubic centimeters (cc) or more. Oversized metal woods generally provide a larger sweet spot and a higher inertia, which provides greater forgiveness than a golf club having a conventional head size.
One advantage derived from the use of lighter and stronger metals is the ability to make thinner walls, including the striking face and all other walls of the metal wood club. This allows designers more leeway in the positioning of weights. For instance, to promote forgiveness, designers may move the weight to the periphery of the metal wood head and backwards from the face. As mentioned above, such weighting generally results in a higher inertia, which results in less twisting due to off-center hits.
There are limitations on how large a golf club head can be manufactured, which is a function of several parameters, including the material, the weight of the club head and the strength of the club head and the materials used. Additionally, to avoid increasing weight, as the head becomes larger, the thickness of the walls must be made thinner, including that of the striking face. As a result, as the striking face becomes thinner and thinner, it has a tendency to deflect more and more at impact, and thereby has the potential to impart more energy to the ball. This phenomenon is generally referred to as the xe2x80x9ctrampoline effect.xe2x80x9d A properly constructed club with a thin face can therefore impart a higher initial velocity to a golf ball than a club with a rigid face. Because initial velocity is an important component in determining how far a golf ball travels, this is very important to golfers.
It is appreciated by those skilled in the art that the initial velocity imparted to a golf ball by a thin-faced metal wood varies depending on the location of the point of impact of a golf ball on the striking face. Generally, balls struck in the sweet spot will have a higher rebound velocity. Many factors contribute to the location of the sweet spot, including the location of the center of gravity (CG) and the shape and thickness of the striking face.
Prior golf club heads have attempted to increase the initial or launch velocity of a golf ball by forming a lightweight, flexible face. Manufacturers of metal wood golf club heads have more recently attempted to manipulate the performance of their club heads by designing what is generically termed a variable face thickness profile for the striking face, in particular with the use of lightweight materials such as titanium alloys.
Another approach to reduce stress at impact is to use one or more ribs extending substantially from the crown to the sole vertically across the face, and in some instances also extending from the toe to the heel horizontally across the face. Because the largest stresses are located at the impact point, usually at or substantially near the sweet spot, the center of the face is always thickened and is at least as thick as the ribbed portions.
There have been other configurations and ribs formed on the back of a club face, including one or more thin rings, a power bar, and a cone formation. Multiple thin rings have been attached by various means so as to add mass directly behind the sweet spot, and alternatively a spiral formation has been used, wherein the multiple rings or spiral mass extend from the sweet spot substantially toward the periphery of the face plate. A single thin ring at the sweet spot has been used on an iron club head in conjunction with an added toe mass in order to reposition a point of least rigidity to the center of the face. In this configuration the rigidity of the face is always higher radially outward from the centered ring.
Other club heads have attempted to utilize power bars or cones behind the sweet spot in order to increase the force imparted to a golf ball. These power bars and cones involve significant additional mass extending toward a rear of the club head, thus affecting the club head CG. However, such club heads do not provide a coefficient of restitution (COR) that is at least the minimum value of approximately 0.8 that is sought by today""s golfers.
The COR for a golf club may be informally defined as a function of the ratio of the relative velocities of a golf ball, just prior to and immediately after impact with the golf club head. The COR baseline value of e=0.822 has been established in the United States, and the formal equation also accounts for the relative masses of a specific club head as well as a golf ball, as follows:
Vout/Vin=(eMxe2x88x92m)/(M+m)
(where M is the mass of the club head and m is an average mass of the golf ball population. Vout is the ball rebound velocity and Vin is the incoming velocity of the ball that is shot at the face of the golf club head using an air cannon, for example.)
In each of the foregoing examples, however, there is ultimately a failure to provide significant forgiveness to off-center hits. Each golf club has attempted to increase COR while addressing to various degrees the difficulties in doing so. For these clubs, the point of impact must still be at the sweet spot in order for these clubs to deliver their highest COR, and even the slightest deviation of the impact from the sweet spot will result in a significant loss in ball velocity.
The present invention provides a solution to enable club designers to overcome the problems described above, including a golf club head that exhibits greater forgiveness across a substantial portion of the striking face while continuing to impart high initial velocity to a golf ball.
In a preferred embodiment of the invention, a golf club head having a coefficient of restitution measuring at least about 0.8 is provided. The club head has a body having a toe portion, a heel portion, a sole portion and a crown portion together defining a front opening. An insert is disposed in the opening and has a substantially planar striking surface on a first side, a rear surface on a second side and a periphery for attachment at the opening on the body. This periphery has a top edge, a bottom edge, a first side edge and a second side edge. The striking surface has a balance point at a central region of the insert and each point on the striking surface has a thickness, and the striking surface has a total area on the insert.
The face insert has a first thickness profile between the balance point and the top edge, a second thickness profile between the balance point and the bottom edge, a third thickness profile between the balance point and the first side edge and a fourth thickness profile between the balance point and the second side edge. The first, second, third and fourth thickness profiles similarly have thickness values at first locations encompassing the periphery of the striking face and including minimum values adjacent the edges. The thickness profiles similarly have thickness values at least 1.5 times the minimum values at second locations between the first locations and the balance point, and the second locations include points having maximum thickness values. The thickness profiles similarly have thickness values at third locations in the central region that are less than the values at the second locations but greater than the minimum values at the first locations.
The first, second, third and fourth thickness profiles in combination represent a substantially annular region of increased thickness comprising the second locations. The thickness values of the third locations form a reduced thickness region, and an area including the substantially annular region and the reduced thickness region extend about 50% of the distance from the balance point to each of the top and bottom edges and the first and second side edges.
Alternatively, a golf club head of the present invention may comprise a body defining a toe portion, a heel portion, a sole portion, a crown portion, and a face portion. The face portion has a striking surface on an outer side and a periphery substantially adjacent a first junction at the face and crown portions, a second junction at the face and sole portions, a third junction at the face and toe portions, and a fourth junction at the face and heel portions. The striking surface has a total area as measured on its outer side, and it has a balance point at a central region of the face portion.
Each point on the striking surface has a local cross-sectional bending stiffness such that the face portion has a first stiffness profile between the balance point and the first junction and a second stiffness profile between the balance point and the third junction. The first and second stiffness profiles similarly have low first stiffness values at first locations that are farthest from the balance point and that encompass the periphery of the striking face. The first and second stiffness profiles similarly have high second stiffness values at second locations that are between the periphery and the balance point, and the first and second stiffness profiles similarly have third stiffness values at the central region.
The face portion is substantially symmetric about central vertical and horizontal axes such that the first stiffness profile also applies between the balance point and the second junction, and the second stiffness profile applies between the balance point and the fourth junction. The first stiffness values include minimum values adjacent the first, second, third and fourth junctions, with the first stiffness values increasing to less than about 3.4 times the minimum values. The second stiffness values are at least about 3.5 times the minimum values, and the third stiffness values are greater than the minimum values and less than about 3.5 times the minimum values. The second and third stiffness values comprise an area of the striking surface that extends approximately halfway from the balance point to the first, second, third and fourth junctions.
In another embodiment of the present invention, a face insert for a golf club head comprises a substantially planar striking surface on a first side of the insert, a rear surface on a second side and a periphery for attachment to the golf club head. The periphery has a top edge, a bottom edge, a first side edge and a second side edge. The striking surface has a balance point at a central region of the face insert and each point on the striking surface has a local cross-sectional bending stiffness. The striking surface has a total area on the first side of the insert.
The face insert has a first stiffness profile between the balance point and the top edge, a second stiffness profile between the balance point and the bottom edge, a third stiffness profile between the balance point and the first side edge and a fourth stiffness profile between the balance point and the second side edge. The first, second, third and fourth stiffness profiles have stiffness values at first locations that encompass the periphery of the striking face and include minimum values adjacent the edges. The stiffness profiles have stiffness values at second locations between the first locations and the balance point that are at least 3.5 times the minimum values which are generally located at the periphery. The second locations include points having maximum stiffness values, and the stiffness profiles have stiffness values at third locations in the central region that are less than the values at the second locations but greater than the minimum values at the first locations.
The first, second, third and fourth stiffness profiles in combination represent a substantially annular region of high stiffness comprising the second locations. The stiffness values of the third locations form a reduced stiffness region including a point having a local minimum stiffness value. The substantially annular region comprises at least about 12% of the total area of the striking surface.
Generally, the present invention can be practiced using a variety of common club head shapes that are known in the art. According to another preferred embodiment of the invention, a hollow metallic body is disclosed. The body has a plurality of thin walls including a toe portion, a heel portion, a sole portion, and a crown portion, wherein all of such portions cooperate to define an interior cavity and to define an opening with a forward edge. A metallic ball striking face is secured to the front edge of the body, using methods that are generally known in the art. This embodiment has a ball string face with substantially uniform wall thickness, as measured from the striking face to the rear surface of the face, except for a portion of the face near the center. Near the center of the face, there is an oblong, washer-shaped region of increased thickness that extends rearwardly into the cavity. The washer-shaped region is preferably formed as an integral part of the rear surface of the striking plate wall, although the washer-shaped region may be fixedly attached to the rear of the face through means known in the art. The washer-shaped region serves to lessen the relative amount of flex in the face and results in a club head that is more forgiving of off-center hits than that of a similar-sized face having a uniform thickness profile. Generally, the region of increased thickness is located radially outward from the sweet spot.